Flip chip mounting method

ABSTRACT

A semiconductor chip ( 15 ) having a pad ( 5 ) covered with a passivation film ( 7 ) is prepared, and the passivation film ( 7 ) over the pad ( 5 ) is selectively removed to expose the pad ( 5 ). Next, a polyimide film ( 11 ) having an opening ( 12 ) for exposing the pad ( 5 ) is formed on the passivation film ( 7 ). Thereafter, solder bumps ( 14 ) are formed on the pad ( 5 ), and an underfill resin ( 17 ) is filled between an assembly substrate ( 16 ) and the semiconductor chip ( 15 ) to bond the assembly substrate ( 16 ) and semiconductor chip ( 15 ) with the solder bumps ( 14 ) interposed therebetween.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a flip chip mounting method, andmore particularly to a method of manufacturing a flip chip prior tobeing mounted.

[0003] 2. Description of the Background Art

[0004] With a flip chip mounting method for bonding a semiconductor chipand an assembly substrate with solder bumps interposed therebetween,stress concentrates on the solder bumps with thermal change and impactoccurring after bonding, causing the solder bumps to be stripped fromthe semiconductor chip or assembly substrate.

[0005] Thus, a method has been employed by which an underfill resin isfilled between a semiconductor chip and an assembly substrate in orderto ease concentration of stress on solder bumps and to promote adhesionbetween the semiconductor chip and assembly substrate (e.g., JapanesePatent Application Laid-Open No. 2002-203866; FIG. 1).

[0006] For flip chip mounting, a pad covered with a passivation filmneeds to be exposed from the passivation film in order to form solderbumps on the side of a semiconductor chip.

[0007] As a method of exposing a pad, a method has been employed bywhich a polyimide film having an opening above the pad is formed on apassivation film, and an etching process is carried out using thepolyimide film as a mask to form an opening in the passivation film soas to reach the pad, thereby exposing the pad from the bottom of theopening.

[0008] With this method, however, a reaction product generated in theetching process carried out on the passivation film adheres to thesurface of the polyimide film, causing a cured layer to be formed on thepolyimide film.

[0009] In the case where the semiconductor chip and assembly substrateare bonded by flip chip mounting using an underfill resin with the curedlayer formed on the polyimide film, adhesion between the underfill resinand cured layer is poor, which problematically causes the assemblysubstrate and semiconductor chip to be stripped from each other duringdevice operation.

[0010] Poor adhesion between the assembly substrate and semiconductorchip had not been in question with semiconductor chips having smallerarea, but has become perceived as a problem with a recent trend towardlarger area of semiconductor chips. This is because stresses have becomeincreased with increase in area of semiconductor chips to such a degreethat frequent splitting of the assembly substrate and semiconductor chipfrom each other due to poor adhesion therebetween cannot be neglected.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide a flip chipmounting method by which a semiconductor chip and an assembly substrateare not readily stripped from each other in the case where thesemiconductor chip and assembly substrate are bonded by a flip chipmethod using an underfill resin.

[0012] According to the present invention, the flip chip mounting methodincludes the following steps (a) through (e). The step (a) is to preparea chip including a pad covered with an insulation film. The step (b) isto selectively remove the insulation film over the pad to expose thepad. The step (c), after the step (b), is to form a polyimide filmincluding a first opening for exposing the pad, on the insulation film.The step (d) is to fill the first opening to form a solder bump on thepad. The step (e) is to fill an underfill resin between an assemblysubstrate and the chip, for bonding the assembly substrate and the chipwith the solder bump interposed therebetween.

[0013] When removing the insulation film, a reaction product of theinsulation film does not adhere to the surface of the polyimide film.Therefore, reduction in adhesion of the semiconductor chip and assemblysubstrate to the underfill resin due to the reaction product can beprevented, allowing adhesion between the chip and assembly substrate tobe promoted.

[0014] These and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIGS. 1 through 6 are explanatory sectional views of manufacturingsteps of a chip according to a first preferred embodiment of the presentinvention;

[0016]FIG. 7 is a sectional view illustrating a semiconductor chip as awhole;

[0017]FIGS. 8 and 9 are sectional views illustrating a flip chipmounting method;

[0018]FIG. 10 is a sectional view illustrating manufacturing steps ofthe chip according to the first preferred embodiment;

[0019]FIG. 11 is a sectional view illustrating the structure of a chipaccording to a variant of the first preferred embodiment;

[0020]FIGS. 12 through 17 are explanatory sectional views ofmanufacturing steps of a chip according to a second preferred embodimentof the invention;

[0021]FIGS. 18 through 21 are explanatory sectional views ofmanufacturing steps of a chip according to a third preferred embodimentof the invention; and

[0022]FIGS. 22 through 24 are explanatory sectional views ofmanufacturing steps of a chip according to a fourth preferred embodimentof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention is characterized by a method of removing apassivation film covering the upper surface of a pad using a resist as amask rather than using a polyimide film as a mask, then forming apolyimide film, forming a solder bump on the pad, and bonding asemiconductor chip and an assembly substrate by a flip chip method usingan underfill resin.

[0024] The present invention will specifically be described referring tothe accompanying drawings showing preferred embodiments of theinvention.

First Preferred Embodiment

[0025] A first preferred embodiment is directed to the case of using asingle-layer passivation film. A flip chip mounting method according tothe present embodiment will specifically be described referring tosectional views showing manufacturing steps.

[0026]FIG. 1 illustrates part of the surface of a semiconductor chipbefore or after being separated from a wafer. As shown, a copperinterconnect line 2 is provided in the surface of an interlayerinsulation film 1, and an insulation film 3 is formed to cover theinterlayer insulation film 1 and copper interconnect line 2. Next, partof the insulation film 3 covering the copper interconnect line 2 isremoved to form a recess 4 in the surface of the insulation film 3, sothat the copper interconnect line 2 is exposed from the bottom of therecess 4.

[0027] Next, as shown in FIG. 2, a pad 5 made of aluminum or the like isformed to cover the bottom and side surfaces of the recess 4 and part ofthe upper surface of the insulation film 3 near the recess 4, and a fuse6 made of aluminum or the like is further formed on the surface of theinsulation film 3 separately from the pad 5. Thereafter, a passivationfilm 7 (a kind of insulation film) is formed by CVD method or the liketo cover the insulation film 3, pad 5 and fuse 6. Here, the passivationfilm 7 is, e.g., a silicon oxide film or the like, having such athickness that allows blowing of the fuse 6.

[0028] Next, as shown in FIG. 3, a resist 8 is coated to cover thepassivation film 7, and exposure and development is performed to form anopening 9 in the surface of the resist 8 above the pad 5. Thepassivation film 7 is exposed from the bottom surface of the opening 9.

[0029] Next, anisotropic etching is performed using the resist 8 as amask to selectively remove the passivation film 7, for forming anopening 10. Thereafter, the resist 8 is removed as shown in FIG. 4. Asis seen from FIG. 4, the pad 5 is exposed from the bottom surface of theopening 10 with this step.

[0030] Next, a photosensitive polyimide film 11 is coated to cover thepad 5 and passivation film 7, and exposure and development is performedusing a mask (not shown) having openings above the pad 5 and fuse 6,respectively, for forming openings 12 and 13 in the surface of thepolyimide film 11. The mask is thereafter removed, and the polyimidefilm 11 is subjected to curing to obtain the structure shown in FIG. 5.As is seen from FIG. 5, the passivation film 7 and polyimide film 11 areabsent above the pad 5 (where the opening 12 is provided) and only thepassivation film 7 is formed over the fuse 6 (where the opening 13 isprovided).

[0031] Next, a solder bump 14 is formed on the pad 5 to fill the opening12 using a plating method which has conventionally been employed. FIG. 6shows the solder bump 14 as formed. FIG. 7 is a general view of asemiconductor chip 15 with solder bumps 14 formed thereon.

[0032] Next, the semiconductor chip 15 is disposed such that the surfaceon which the solder bums 14 are formed faces a mounting surface of anassembly substrate 16 and is bonded to the mounting surface of theassembly substrate 16 by the flip-chip method. The way of bonding isshown in FIG. 8.

[0033] Finally, as shown in FIG. 9, an underfill resin 17 is poured(filled) between the semiconductor chip 15 and assembly substrate 16.

[0034] The underfill resin 17 functions as adhesive as well as stressrelieving material. Thus, the underfill resin 17 can promote adhesionbetween the semiconductor chip 15 and assembly substrate 16 connectedwith the solder bumps 14 interposed therebetween and relieveconcentration of stress on the solder bumps 14 occurring during deviceoperation.

[0035] Among methods of filling the underfill resin 17 are a method ofpouring the underfill resin 17 into the gap between the semiconductorchip 15 and assembly substrate 16 and a method of previously coating theunderfill resin 17 on the mounting surface of the assembly substrate 16.

[0036] By the flip chip mounting method of the present embodiment asdescribed above, part of the passivation film 7 over the pad 5 isremoved before forming the polyimide film 11, which prevents a reactionproduct generated in removing the part of the passivation film 7 fromadhering to the surface of the polyimide film 11.

[0037] Therefore, as described in the background art, it is possible toprevent reduction in adhesion of the semiconductor chip 15 and assemblysubstrate 16 to the underfill resin 17 due to a reaction product, whichcan promote adhesion between the semiconductor chip 15 and assemblysubstrate 16.

[0038] Although described as having such a thickness that allows blowingof the fuse 6, the passivation film 7 may have a greater thickness.

[0039] In this case, as shown in FIG. 10, a resist 21 having an opening20 is provided above the fuse 6 after the step shown in FIG. 4, and thepassivation film 7 is etched to have such a thickness that allowsblowing of the fuse 6 using the resist 21 as a mask, and the step shownin FIG. 5 is thereafter performed.

[0040] As described, provided that the step of etching the passivationfilm 7 to have such a thickness that allows blowing of the fuse 6, thepad 5 and fuse 6 are not required to be provided in the same layer, butthe fuse 6 may be provided in a layer below the one in which the pad 5is formed as shown in FIG. 11.

[0041] Although described as being a single layer in the abovedescription, the insulation film 3 may be a two-layered film in which asilicon nitride film and a silicon oxide film are stacked in this order.Such silicon nitride film is provided as moisture barrier for layersunder the silicon nitride film.

Second Preferred Embodiment

[0042] A second preferred embodiment is directed to the case of using atwo-layered passivation film (in which a nitride film and an oxide filmare stacked). A flip chip mounting method according to the presentembodiment will specifically be described referring to sectional viewsshowing manufacturing steps. The steps are the same as those in thefirst preferred embodiment as far as the structure shown in FIG. 2 isobtained, repeated explanation of which is thus omitted here. In thepresent embodiment, the first layer of the passivation film is a siliconoxide film 7 a.

[0043] Next, as shown in FIG. 12, a silicon nitride film 7 b is formedas the second layer of the passivation film by the CVD method or thelike to cover the silicon oxide film 7 a. Here, the silicon nitride film7 b functions as moisture barrier for the copper interconnect line 2 andthe like.

[0044] Next, as shown in FIG. 13, a resist 22 is coated to cover thesilicon nitride film 7 b, and exposure and development is performed toform openings 23 and 24 in the surface of the resist 22 above the pad 5and fuse 6. The opening 23 is present above the pad 5 and the opening 24is present above the fuse 6. The silicon nitride film 7 b is exposedfrom the bottom surfaces of the openings 23 and 24.

[0045] Next, anisotropic etching is performed using the resist 22 as amask to selectively remove the silicon nitride film 7 b. Thereafter, theresist 22 is removed as shown in FIG. 14. As is seen from FIG. 14, partof the silicon nitride film 7 b above the pad 5 and fuse 6 has beenremoved.

[0046] Next, as shown in FIG. 15, a resist 25 is coated to cover thesilicon nitride film 7 b and silicon oxide film 7 a, and exposure anddevelopment is performed to form an opening 26 in the surface of theresist 25 above the pad 5. The silicon oxide film 7 a is exposed fromthe bottom surface of the opening 26.

[0047] Next, anisotropic etching is performed using the resist 25 as amask to selectively remove the silicon oxide film 7 a, for forming anopening 27. Thereafter, the resist 25 is removed as shown in FIG. 16. Asis seen from FIG. 16, the pad 5 is exposed from the bottom surface ofthe opening 27 with this step.

[0048] Next, the photosensitive polyimide film 11 is coated to cover thepad 5 and passivation film (7 a and 7 b), and exposure and developmentis performed using a mask (not shown) having openings above the pad 5and fuse 6, respectively, for forming the openings 12 and 13 in thepolyimide film 11. The mask is thereafter removed, and the polyimidefilm 11 is subjected to curing to obtain the structure shown in FIG. 17.As is seen from FIG. 17, the passivation film (7 a and 7 b) andpolyimide film 11 are absent above the pad 5 (where the opening 12 isprovided) and only the silicon oxide film 7 a is formed over the fuse 6(where the opening 13 is provided).

[0049] Formation of the solder bumps 14 and flip chip mounting of thesemiconductor chip 15 and assembly substrate 16 performed thereafter arethe same as those in the first preferred embodiment, repeatedexplanation of which is thus omitted here.

[0050] As described, the flip chip mounting method according to thepresent embodiment, by which the passivation film (7 a and 7 b) areremoved before forming the polyimide film 11, can achieve the sameeffect as described in the first preferred embodiment.

Third Preferred Embodiment

[0051] A third preferred embodiment is also directed to the case ofusing a two-layered passivation film (in which a nitride film and anoxide film are stacked), however, the passivation film is removed withdifferent steps from those in the second preferred embodiment. A flipchip mounting method according to the present embodiment willspecifically be described referring to sectional views showingmanufacturing steps.

[0052] First, a semiconductor chip having the structure as described inthe first preferred embodiment as shown in FIG. 2 is formed, and thesilicon nitride film 7 b is formed over the silicon oxide film 7 a asdescribed in the second preferred embodiment referring to FIG. 12.

[0053] Next, as shown in FIG. 18, a resist 31 is coated to cover thesilicon nitride film 7 b, and exposure and development is performed toform an opening 32 in the surface of the resist 31 above the pad 5. Thesilicon nitride film 7 b is exposed from the bottom surface of theopening 32.

[0054] Next, anisotropic etching is performed using the resist 31 as amask to selectively remove the silicon nitride film 7 b and siliconoxide film 7 a, for forming an opening 33. Thereafter, the resist 31 isremoved as shown in FIG. 19. As is seen from FIG. 19, the pad 5 isexposed from the bottom surface of the opening 33.

[0055] Next, the photosensitive polyimide film 11 is coated to cover thepassivation film (7 a and 7 b) and pad 5, and exposure and developmentis performed using a mask (not shown) having openings above the pad 5and fuse 6, respectively, for forming openings 34 and 35 in thepolyimide film 11. The mask is thereafter removed, and the polyimidefilm 11 is subjected to curing to obtain the structure as shown in FIG.20. As is seen from FIG. 20, the passivation film (7 a and 7 b) andpolyimide film 11 are absent above the pad 5 (where the opening 34 isprovided) and only the passivation film (7 a and 7 b) is formed over thefuse 6 (where the opening 35 is provided).

[0056] Next, anisotropic etching is performed using the polyimide film11 as a mask to selectively remove the silicon nitride film 7 b, forforming an opening 36 as shown in FIG. 21. As is seen from FIG. 21, thesilicon oxide film 7 a is exposed from the bottom surface of the opening36.

[0057] Formation of the solder bumps 14 and flip chip mounting of thesemiconductor chip 15 and assembly substrate 16 performed thereafter arethe same as those in the first preferred embodiment, repeatedexplanation of which is thus omitted here.

[0058] As described, with the flip chip mounting method according to thepresent embodiment, removal of the silicon nitride film 7 b above thefuse 6 using the polyimide film 11 as a mask causes a reaction productof the silicon nitride film 7 b to adhere to the surface of thepolyimide film 11.

[0059] However, since a reaction product of the silicon nitride film 7 bhave better adhesion to the underfill resin 17 than a reaction productof the silicon oxide film 7 a, adhesion between the semiconductor chip15 and assembly substrate 16 can be promoted in the present embodimentas well (though not better than in the other preferred embodiments).

[0060] Further, employing the flip chip mounting method according to thepresent embodiment (that is, removing the silicon nitride film 7 b usingthe polyimide film 11 as a mask), the number of resists can be reducedby one as compared to the second and fourth preferred embodiments,leading to simplification of the flip chip mounting method, which cancut down manufacturing costs.

Fourth Preferred Embodiment

[0061] A fourth preferred embodiment is also directed to the case ofusing a two-layered passivation film (in which a nitride film and anoxide film are stacked), however, the passivation film is removed bydifferent steps from those in the second and third preferredembodiments. A flip chip mounting method according to the presentembodiment will specifically be described referring to sectional viewsshowing manufacturing steps.

[0062] First, the semiconductor chip having the structure described inthe first preferred embodiment as shown in FIG. 2 is formed, and thesilicon nitride film 7 b is formed over the silicon oxide film 7 a asdescribed in the second preferred embodiment referring to FIG. 12.Thereafter, as described in the second preferred embodiment referring toFIGS. 18 and 19, the passivation film (7 a and 7 b) above the pad 5 isremoved.

[0063] Next, as shown in FIG. 22, a resist 41 is coated to cover the pad5 and passivation film (7 a and 7 b), and exposure and development isperformed to form an opening 42 in the surface of the resist 41 abovethe fuse 6. The silicon nitride film 7 b is exposed from the bottomsurface of the opening 42.

[0064] Next, anisotropic etching is performed using the resist 41 as amask to selectively remove the silicon nitride film 7 b, for forming anopening 43 as shown in FIG. 23. As is seen from FIG. 23, the siliconoxide film 7 a is exposed from the bottom surface of the opening 43.

[0065] Next, after removing the resist 41, the photosensitive polyimidefilm 11 is coated to cover the pad 5 and passivation film (7 a and 7 b),and exposure and development is performed using a mask (not shown)having openings above the pad 5 and fuse 6, respectively, for formingthe openings 12 and 13 in the polyimide film 11. The mask is thereafterremoved, and the polyimide film 11 is subjected to curing to obtain thestructure shown in FIG. 24. As is seen from FIG. 24, the passivationfilm (7 a and 7 b) and polyimide film 11 are absent above the pad 5(where the opening 12 is provided) and only the silicon oxide film 7 ais formed over the fuse 6 (where the opening 13 is provided).

[0066] Formation of the solder bumps 14 and flip chip mounting of thesemiconductor chip 15 and assembly substrate 16 performed thereafter arethe same as those in the first preferred embodiment, repeatedexplanation of which is thus omitted here.

[0067] As described, the flip chip mounting method according to thepresent embodiment, by which the passivation film (7 a and 7 b) areremoved before forming the polyimide film 11, can achieve the sameeffect as described in the first preferred embodiment.

[0068] The present embodiment has been directed to the case of applyingthe flip chip mounting method of the present invention to the structurein which the pad 5 and fuse 6 are covered with the passivation film 7 (akind of insulation film).

[0069] However, the present invention may also be applied to thestructure in which the pad 5 and fuse 6 are covered with a film merelycalled insulation film, not passivation film. That is, in flip chipmounting, manufacturing steps may be carried out in the order that acertain part of the insulation film is removed before forming thepolyimide film 11.

[0070] Here, an insulation film, in a broad sense, involves a filmcalled passivation, a kind of insulation film, and an insulation film ina narrow sense (i.e., a film merely called insulation film, notpassivation film).

[0071] Although the above preferred embodiments have been directed tothe semiconductor chip having the fuse 6, the fuse 6 may not necessarilybe provided in view of the characteristics of the present invention thatpart of the passivation film (insulation film) 7 over the pad 5 isremoved before forming the polyimide film 11.

[0072] However, by applying the flip chip mounting method of the presentinvention to the semiconductor chip 15 having the fuse 6, adhesionbetween the semiconductor chip 15 and assembly substrate 16 can bepromoted without making fuse blowing difficult in a device havingredundancy.

[0073] While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A flip chip mounting method comprising the stepsof: (a) preparing a chip including a pad covered with an insulationfilm; (b) selectively removing said insulation film over said pad toexpose said pad; (c) after said step (b), forming a polyimide filmincluding a first opening for exposing said pad, on said insulationfilm; (d) filling said first opening to form a solder bump on said pad;and (e) filling an underfill resin between an assembly substrate andsaid chip, for bonding said assembly substrate and said chip with saidsolder bump interposed therebetween.
 2. The flip chip mounting methodaccording to claim 1, wherein said chip prepared in said step (a)further includes a fuse covered with said insulation film, said step (b)further includes the step of selectively removing said insulation filmabove said fuse, and said polyimide film formed in said step (c) furtherincludes a second opening formed above said fuse.
 3. The flip chipmounting method according to claim 2, wherein said insulation film is apassivation film in which an oxide film and a nitride film are stackedin this order, and said step (b) includes the steps of: (b-1)selectively removing said nitride film above said pad and selectivelyremoving said nitride film above said fuse; and (b-2) after said step(b-1), selectively removing said oxide film above said pad, for exposingsaid pad.
 4. The flip chip mounting method according to claim 2, whereinsaid insulation film is a passivation film in which an oxide film and anitride film are stacked in this order, said nitride film and oxide filmover said pad are selectively removed in said step (b), and said flipchip mounting method further comprising the step of (f) after said step(c), selectively removing said nitride film above said fuse using saidpolyimide film as a mask.
 5. The flip chip mounting method according toclaim 2, wherein said insulation film is a passivation film in which anoxide film and a nitride film are stacked in this order, and said step(b) further includes the steps of: (b-3) selectively removing saidnitride film and oxide film over said pad, for exposing said pad; and(b-4) selectively removing said nitride film above said fuse using amask which covers said pad as exposed.